1. Field of the Invention
The present invention relates to a sheet post-processing apparatus used for cutting off an edge of a booklet produced by performing center folding in a process to bind sheets of paper, and an image forming apparatus and an image forming system that include the sheet post-processing apparatus.
2. Description of the Related Art
In the related art, in the field of printing, a sheet post-processing apparatus that includes a cutting device is practically used in which the cutting device cuts off an edge of a booklet that has passed through a saddle stitching process and a center folding process and performs edge alignment. In addition, recently, a sheet post-processing apparatus that includes a cutting device has been produced. The sheet post-processing apparatus receives sheets of paper with images thereon formed by an image forming apparatus such as a copying machine or a printer, performs a saddle stitching process and a center folding process, performs binding to produce, for example, a weekly magazine-like form, and allows the cutting device to cut off the edge of the booklet and to perform edge alignment.
In the cutting device described above, a booklet that has been produced through a saddle stitching process and a center folding process is conveyed by a conveying unit such as a belt such that a folded portion of the booklet becomes a leading edge in a conveying direction. Then, the booklet is stopped by abutting on an abutting member, and pressed at a portion near the folded portion by a first pressing unit and a portion near the edge by a second pressing unit, respectively. In this state, the edge is cut off by the cutting device. As a method for setting a position of the booklet when cutting is to be performed in this kind of an apparatus, there is a known position setting method according to which the booklet is stopped when the folding portion of the booklet abuts on a leading edge stopper, the leading edge stopper is moved toward the folded portion of the booklet, and the position of the booklet is set while posture of the booklet is corrected.
However, in the position setting method in the cutting device of the related art, there has been a problem in that the frictional force occurring between the conveying member and the booklet when the booklet slides on the conveying member is strong to cause defects such as cover peeling or an opposite arrangement between a right page and a left page when the booklet is opened after the edge has been cut off, thereby impairing the finishing quality of a sheet bundle.
Japanese Patent Application Laid-open No. 2010-195582 discloses a center-folded booklet conveying apparatus having a simplified mechanical structure capable of setting a position of a saddle-stitched and center-folded booklet to a predetermined position by a simplified conveying operation. The center-folded booklet conveying apparatus includes a booklet conveying unit that conveys a booklet having a saddle-stitched and center-folded portion and made of a plurality of sheet members in a state where the booklet is stacked on a booklet stacking member and a booklet position setting unit having a booklet abutting member for abutting on the center-folded portion and capable of reciprocating in a booklet conveying direction. The booklet is stopped when the position of the center-folded portion of the booklet having been conveyed by the booklet conveying unit is set at a downstream side of a predetermined position in the booklet conveying direction, and thereafter, the abutting member is moved the downstream to an upstream side in the booklet conveying direction to abut on the center-folded portion and further to press center-folded portion backwards in the booklet conveying direction, thereby to set the position of the booklet to the predetermined position by sliding the booklet on the stacking member.
However, the problems caused by the strong frictional force between the conveying member and the booklet have not been unresolved yet. That is, defects such as cover peeling or an opposite arrangement between a right page and a left page when the booklet is opened after the edge has been cut off deteriorates the finishing quality of a bundle of sheets.
Therefore, there is a need to improve the quality of a booklet by retracting a conveying member with a large coefficient of friction when the position of the booklet in the cutting device is to be set, by reducing a frictional force associated with the conveyance of the booklet accomplished by letting the booklet slide on a different supporting member than the conveying member, and by achieving stability in conveying the booklet.